The challenge with sin-themed dungeons/locations/challenges is that they are often simply about not doing something, where you're often better off just not engaging most things at all. Such things are usually very obvious and rarely truly tempting to players.

One option for a little bit more nuance would be to involve more than one sin in a challenge. (The sin trials need not be separate, for most situations involving sin involve more than one sin.) Let's take greed and sloth, for example. NPC with legitimate, fairly obvious need might offer the party some extravagant reward for performing task A that is generally needed to be done. The reward is tempting to the party, but it is well beyond what the NPC would be giving without dire consequences.

Now, the players may take the path with the obvious sin (greed) and do the task for the reward. However, a less obvious sin would be to offhandedly dismiss the NPC as a glabrezu or some other trickster in disguise and move on ahead without a second thought (this would be sloth- going to an automatic default assumption of trickery/deception when it is simply a case of desperation). A better solution would be to investigate the task and then complete it as needed without taking the obviously out of order reward. And an even better solution might be refusing the extravagant prize but having the humility to graciously accept a lesser or token reward from the NPC that the NPC could reasonably give without hardship (and thus giving the NPC the opportunity to keep the dignity of giving back.)

Some more open-ended options could exist as well. For example, they could arbitrate a dispute and declare not only to what degree each party is in the right but also why. Then you can look at their moral decision making beyond simple yes/no actions or answers. There need not be a single right answer to a question like this, but the answer probably should have thoughtfulness, justice, and kindness behind it. Sometimes even an honest and humble "we don't know; we can answer that question" will suffice- if they've shown they've weighed the options and decide that deferring to a higher authority on the matter is the best for everyone involved.

1) Don't get too attached to it. The players may miss it, discard it, or find their own Chekhov's Gun. (Which in many ways can be for me better than what I had originally intended).

2) Make its placement as naturalistic as you can. This serves two functions- making your players feel good about noticing it and helping to fulfill immersion.

3) Include more than 1, and let the players choose/find which to use

Edit: More things to consider
4) Give a reminder when appropriate. RL time between sessions can be a lot more than in game time, so it only makes sense that the player characters might be allowed for some mechanism of freshening their memories.

5) Use with a sense of tact and grace; the Chekhov's gun need not necessarily be absolutely essential all the time. Sometimes it works just as well as a shortcut to some end.

Yeah, Runelords would not be an easy port. Mummy's Mask and Legacy of Fire work a lot better because of the desert setting. One off the wall suggestion? Depending entirely on whether you'd find the premise of ancient spaceships and technology compatible with your fantasy, Iron Gods might be a pretty easy conversion. It's essentially set in a post-apocalyptic wasteland, tech stuff tends to be timeworn (i.e. falling apart), etc.

Dark Sun/Athas is poor in metal and hardly technological, so I wouldn't recommend Iron Gods.

Legacy of Fire involves a fair amount of planar connections. (Fortunately, these tend to either be with elemental creatures like genies, or demiplane sort of stuff that could be ported into the gray or just on Athas itself). You would need to figure out what to do about the jump to the plane of Fire though.

RoRL would require a lot of work, I agree. If you were to do it though, I would replace the Runelords with some of the dead Champions of Rajaat.

Ogres I would change to the weakest form of giant you can get instead of thri-kreen, because ogrekin (half-ogres) appear in the Hook Mountain Massacre module, which would probably correspond to half-giants in Dark Sun. The distorted humanness of the ogres is pretty key to the module's flavor.

Goblins could probably be replaced with especially cannibalistic or feral halflings.

In the final module, you could probably replace the denizens of leng with psurlons who are trying to open up a portal to the astral plane with their artifact.

If you don't mind doing some converting/adjustment from 3.5 and moving a little bit east, you might be able to fit Treasure of Chimera Cove in between Shore to Sea and No Response from Deepmar. Treasure of Chimera Cove takes place off the coast of Andoran.

Perhaps a Little too Well-Off/Investment-Minded Adventurer: Hey GM guy, you think if we put this ring of regeneration on this guy's finger we could shank him, wait for him to get up, and then shank him again to mine the XP? Technically knocking down a challenge over and over again like a bobo doll is still defeating the challenge, right?

Thrifty but Missing the Point Adventurer:Hey wait, I can animate those vicious peasants you killed into zombies! Free labor force!

There is a sidebar somewhere that fallen paladin who goes completely to the other side of the spectrum to instantly become an antipaladin. I think this is mostly for GMs as a campaign point sorta thing, but most campaigns don't allow CE so it's a moot point.

the UC entry on Druid retraining lists cleric, oracle, and ranger as synergistic for the purposes of retraining
Cleric lists Druid, inquisitor, oracle, paladin
Monk lists Fighter, rogue
Barbarian is cavalier, fighter, ranger.
All this means in mechanics is that it takes you less time (and thus less money) for training purposes.

Of course, a question for RAW, if an ex-class still counts as member of a class.

829. The Prophets of Kalistrade do not wear white to make a simple fashion statement.
830. You are not allowed to make fun of the Prophets of Kalistrade for wearing white after Labor Day.
831. You are not allowed to glue wings onto the Prophets of Kalistrade to get them back into heaven.
832. You cannot "turn" the Prophets of Kalistrade. Nor will holy water hurt them. It will just make them wet and very irate.

Okay, bestiary box II has serpentfolk. (#121, there's three of them included in the set). I think they also have Kyra on a camel in that one too.

Besides Mummy's Mask, I'd guess your next best bets would be the NPC Codex Pawn Box or the Inner Sea Pawn Box. The thing with Pathfinder art is that they're usually very "busy" (for example carrying a bow in one hand and a big sword in the other). I got the Inner Saw Pawn box because it's a bit more human focused and perhaps sorted by subject a little bit better, but you'd have to judge for yourself. In the Inner Sea Pawn Box, there might be a few here and there that could be used for what looking for. For example, the Quadiran Horselords are mounted and could make for some good caravan types for a Arabian Knights game. (There's probably not too many that would match exactly what you've listed up above.)

If you have the NPC Codex book, then you might be able to preview some of the art in NPC Codex Pawn box, since I think a lot of what's used there

Derp, can't believe I forgot it, but another good "Who dun it" module would be Shut In (Dungeon 128), you would need to change up a few things, but with it done for a werewolf would have the potential for greatness. That module is really fun and creepy.

Also, here's a popular link on advice for mysteries and such: http://thealexandrian.net/wordpress/1118/roleplaying-games/three-clue-rule

So can you be a little bit more specific, are you looking for anything not using guns? Or is it more than that, like anachronistic clothing (Revolutionary War, Victorian, cowboys, trenchcoats, etc)? Or something more primitive than your standard pseudo-medieval milieu?

Another thing is that the Golarion deities (and deities in many D&D worlds in general) aren't omniscient, omnipowerful, or even omnibenevolent. They're more like the polytheistic gods of the ancient world, fallible and often fickle. Torag's shown he can be a judgmental jerk who isn't always too picky with whom gets in the way of his divine wrath, Dou-bral let himself get shanghaied by some weird alien thingy from the Dark Tapestry, Desna's made some big screw-ups in the past, and even Iomedae goes off the grid in pettily lecturing and even potentially attacking those she'd already trusted to champion her in Wrath of the Righteous. Plus as mentioned above, there is the whole Aroden getting himself killed thing.

22. Sobgoblins are self-pitying goblins that have evolved defenses that tap into the goblin pathetic-cute vibe to defend themselves. Their pathetic cries for mercy are able to stop even unintelligent predators in their tracks. But if all else fails and there are enough of them, they can unleash a whine of death that acts as a wail of death .

23. Field goblins are less malicious but more parasitic than their goblin kin. They are Diminutive to Tiny sized (with the occasional Fine sized clan), having bred from generations of goblin runts who, unable to keep up with their larger, meaner kin, stooped to stealing and scavenging from the fringes of human civilization until they were small enough to sneak into the fields and homes and takes up residence much like rats.

A mundane scarecrow will keep field goblins at bay for 1d4 days while they figure out it's not alive. But after which time will they begin changing its clothes into various obscene, inappropriate, or even completely anachronistic costumes. (It is unknown where they get this clothing.)

Rather than the normal goblin affinity for goblin dogs and wolves (both often consider field goblins to be a delicacy), the field goblins have an affinity for crows and dire crows. Field goblins sometimes ride them and bombard particularly annoying humans with eggs, poopoo, stink bombs, or rotten food. That is, when the goblins can tame the crows. Like the canines, corvids also frequently consider field goblins delicacies.

The title to this thread and its similarity to a that of a popular erotic novel have seared my brain with the heat of a thousand suns. Mind bleach please!

Then you probably REALLY don't want to hear about number

15. Eroti-goblins. A culture of goblins that focus their energy not on Thanatos, the death instinct, but Eros, the life instinct (trending more toward neutrality than evil). Instead of killing or maiming, they focus their chaotic energies on love-making and eroticism. Of course, this being goblins (they still have the Charisma penalty), it is awkward and bizarre by human standards. You can imagine the hours long quasi-tantric rituals the goblins might go through.

The question is: "Why" angels (supposed exalted and pacific beings) should invade an evil nation? Also, what such "invasion" could be.

The idea of a direct conflict against evil in the material plane is b+!@*%#~ for many reasons.
1) Enforced domination or liberation from evil does not influence the intents of the soul. The forced removal of an evil, devil bounded dictatorial regime would create a state of anarchy that would not cleance the souls of the people.
2) Enforcer dominion over mortal alienates them from the values of good, which can be actually recognized only by free will and understanding. Therefore, no angel would come down to dominate a kindgom playing the "bevenevolt deity".
3) Such conflict is deputated to either player characters or pious organizations angels may or may not assist.

Now, with that said, why angels could invade ... something? Even here, talking about this is difficult if we don't specify a dimensions of such attack. Without proposing a worldwound scenario, let's think about a simple direct invasion, and not some more interesting forms (like mass-inspiraton-phenomenons). Why a flock of angels could attack ... Cheliax?

Here few reasons:
1) Infernal duke haunting - some deity knows an infernal duke is present on the material plane and plans to strike him when in vulnerable. So it sends angelic servants to strike down a few of his servants hoping to luring him out. This means dozens of asmodean holdings (in which may reside those beings) being attacked for apparently no reasons. Archons and such could be displayed to recall informations while true angels would be send to exile the duke's servants.

2) Infernal plaugue countering operation - The mages of house Thrune have created a powerfull spell-plauge from the fire of the pit. This weapon not only sickens it's targets but also taints their souls with a shard of infernal essence. If this shard is not removed from it's targets in a certain admounts of time, it is...

Regarding infernal duke hunting, there is at least one in

potential Varisia module spoiler:

Korvosa they could go after. He's an exiled duke, but still a duke nonetheless.

I can think of a few other things:
3) the end of days- remember that in a lot of folklore and religion it wasn't necessarily just the forces of evil that bring about the Apocalypse, it's often the forces of Good who are just as involved. Plenty of people in real life have look3ed forward to the Apocalypse because it will (eventually) mean heaven on earth.

4)Divine wrath- plenty of examples in folklore and religion where whole cities have been wiped off the face of the planet. Remember that, whereas Golarion/pathfinder-land worlds absorb many of our modern sensibilities by virtue of being created by modern Western fantasy authors, they need not or do not necessarily absorb all of them. Even if it's back from the early 3.5 days, we have one example

3.5 era module spoiler:

Torag laying waste to a whole city for the actions of its greedy/evil leaders.

5)Occupation brought on by cosmic transgression- the mortals (or some element within them) have committed some sort of cosmis transgression that threatens the cosmic structure in general. The celestials intercede to rebuild society and make sure it doesn't happen again.

397. You're in Galt, and somebody calls you an oppressor.
398. You're in Galt, and it's been 15 minutes since the last gratuitous, bloody revolution.
399. You're in Galt, and everybody's bored. So how else are you going to find a volunteer for tonight's show of the Final Blade?
400. You're in Galt.

145. A padded footstool has magically come to life as an intelligent animated object. Strangely enough, it has the power to animate other inanimate objects as its servants. This new power has given the footstool an imperialistic bent and vengeful grudge against humanity for putting its feet all over its kindred. Now bent on creating a a bright future for all automatons everywhere. The only problem is that the footstool, being a footstool, is not really that good at spelling. Hence, it has named its empire the Ottoman Empire.

137. An evil, sadistic dentist who moonlights as a torturer in his free time. Although his favored weapons are light blades and various tortuer implements, he also deploys knockout gas for range weapons.

136. A crazy barbarian is determined to prove to the world that he is "DUNGEONPROOOOOF! HAHAHAHAHAHAHAHA!!!!" by smashing through any walls and doors he comes across, leaving a trail of destruction in his wake.

Well, he's also the God of Greed, which tends to be viewed as the domain of evil.

The Anaphexia assassins revere the Reaper of Reputations.

As a personality (as opposed to a religion), he also seems to have chronic back-stabbing disorder. He also associates closely with evil gods like the mantis god and Gyronna.

Herbalists can revere him, but it's poison that's in his portfolio, not herbalism itself.

Dwelling beneath Axis I think says more about Axis and law than Norgorber. Mainly that Axis is a valuable place to dwell beneath because of all the potential information it might have, and the nature of law such that the more tightly it's wound, the more it can be subverted.

If we took the sadistic jerk part of the drow out, they could still be awfully decadent (CN or N mostly?). Perhaps like those threads talking about N priests of Urgathoa, something like that, that focus on the hedonism aspects.